Coupling means



July 26, 1966 J. w. SULLIVAN ETAL 3,263,194

COUPLING MEANS Filed Aug. 24, 1964 United States Patent O 3,263,194 COUPLING MEANS .lohn W. Sullivan, Los Altos, and Robert J. Twiggs, Sunnyvale, Calif., assignors to Varian Associates, Palo Alto, Calif., a corporation of California Filed Aug. 24, 1964, Ser. No. 391,722 8 Claims. (Cl. S33-97) This invention relates to coupling means. While not limited thereto, the invention has utility as a coupling means for electron discharge devices of the slow wave type employing fluid cooling internal to the slow wave structure.

State-of-the-art traveling wave tubes comprise: an evacuated envelope; an electron lgun disposed at one end of the envelope for producin-g and directing an electron stream along a predetermined pat-h; a slow-wave structure, typically a conductive helix disposed about the path for propagating electromagnetic waves for inter-action with the electron stream; and, a collector assembly at the opposite end of the tube in which the electron st-ream is ultimately absorbed. An input signal to be amplified is coupled to the upstream end of the slow-wave struct-ure while the amplified output signal is transferred -to a load-circuit coupled to the downstream end of the slow-wave structure.

The output of high power traveling wave tubes has been limited in the past due to heating caused by a number of factors such as the helix intercepting part of the current in the electron stream, R.F. power dissipation at the output end lof the helix and the introduction of lossy materials to attenuate waves refiected lfrom the output end. As the temperature of the helix rises, its resistance increases substantially, thereby severely limiting power output. If the helix becomes too ho-t, metal may evaporate Ifrom it and spray insulating surfaces. This can ca-use RF. attenuation. If the helix is supported on dielectric -rods and these rods become too hot, RF. attenuation may occur. Various schemes have been devised, having for their purpose cooling of slow-wave struc-tures whereby R.F. power output of a ygiven tube may be greatly increased. Among the more promising of these schemes has been the utilization of a hollow slow-wave structure or helix through which a fluid coolant is circulated. It is necessary in those tubes which employ fiuid cooling internally of the slow-wave structure to provide -a means for couplin-g RF. energy to the upstream end of the tube and a means for extracting the amplified output signal, which means are capable of keeping separate the fluid coolant and the R.F. energy in such a manner as to produce a very small perturbation in the coupling means. Those coupling means characteristic of the prior art have not proved to be entirely satisfactory because of their inherent narrow band properties due, for example, to the presence in the coupling means of `a frequency sensitive impedance matching element such as a quarter wavelength matching stub.

It is the object of the present invention to provide a broad band RF. coupling means useful, for example, i-n connection with electron discharge devices of Athe slowwave type employing fluid cooling internally of the slowwave structure, and which is capable of separating the RF. energy and fluid coolant within said coupling means with minimum perturbation.

Briefiy stated, in accordance with one teaching of the present invention, there is disclosed an RF. coupling means useful, for example, in either coupling RJF. energy to the upstream end of an internally cooled slow-Wave structure or traveling wave tube, or extracting the amplified output from the structures downstream end. The means comprises: -a hollow T-shaped member formingl an outer conductor and having a pair of arms and a leg; a hollow inner conductor along which R.F. energy may 3,263,194 Patented July 26, 1966 travel and through which a coolant may flow disposed within one arm of the T-shaped member; a dielec-tric pipe through which 4a fluid coolant may flow being in uid communication with said hollow linner conductor and disposed either -Within the leg of the T-shaped member or the other arm of said T-shaped member; and an inner conductor Ialong which RF energy rnay travel being in RF. coupling relation to the hollow inner conductor and disposed within either the other arm of said T-shaped member or the base of the T-shaped member whereby the RF. energy and fluid coolant may be separated within the coupling means with minimum perturbation. The utilization of a dielectric pipe for providing communication between the external fluid coolant supply and the hollow inner conductor permits separation of the R.F. energy and fluid coolant while minimizing R.F. re-fiections due yto impedance discontinuities as is characteristc of the pri-or a-rt. The arms of the T-shaped member are preferably axially aligned while its 'leg is preferably at right angles thereto.

One feature of the present invention is the provision of an RF. coupling means comprising a hollow T-shaped member forming an outer conductor and having a pair of arms and a leg, a hollow inner conductor along which RF. energy may travel and through which a fluid coolant may flow disposed within one arm of said T-shaped member, a dielectric pipe through which a uid coolant may flow, being in fluid communication with the .hollow inner conductor and being disposed within either the other arm or the legs of the T-shaped member and an inner conductor along which RF. energy may travel being in R.F. coupling relation to the hollow inner conductor and disposed either Within the base or the other arm of said T- shaped member.

Another feature of the present invention is the provision of an R.F. coupling means of the above types wherein said arms are -axially aligned and said leg is at right angles with respect thereto.

These and other objects and features of the present invention and a further understanding may be had by referring to the following description and claims, taken in conjunction with the 4following drawing lin which:

FIG. 1 is a longitudinal View, partially broken away, in section of a traveling Wave tube employing the novel coupling means of the present invention;

FIG. 2 is a cross-sectional view of another embodiment of the novel coupling means of the present invention; and

FIG. 3 is a typical plot of frequency vs. VSWR for the input and output coupling means of the type shown in FIG. l.

Referring now to FIG. l there is shown a traveling wave tube 11 employing the novel Vcoupling means of the present invention. Tube 11 is similar to many tubes well known in the art today and will not be described in detail herein except to the extent necessary to indicate utilization of the present invention in connection therewith. The tube 11 includes an elongated envelope 12 having an axially directed bore 13. At one end 0f the envelope 12 is disposed an electron gun unit 14 for producing and directing an electron stream along the axis of the bore 13 toWa-rd a collector assembly 15 on the right hand end or downstream end of the tube 11 where the stream is ultimately absorbed. Between the electron gun unit 14 and collector assembly 15 is disposed a slow-Wave structure 16, a hollow conductive helix disposed about the axis of bore 13 for propagating electromagnetic waves for interaction with the electron stream and which is also adapted to provide passage for a fiuid coolant such as water. A coupling assembly 17 provides a Vmeans for coupling an input signal to be amplified to the upstream end of the slow-wave structure 16 through the intermediary of an input transmission line 18. In the embodiment disclosed the input transmission line 18 is illustrated as being of the coaxial type formed by the inner side wall 19 of an additional axial bore 20 and a hollow inner conductor 21. The amplified output signal is transferred from the downstream end of the slow wave structure 16 through the intermediary of an output transmission line 22 by means of output coupling means 23. The output transmission line 22 is similar to the input transmission line 18, being formed by the inner side wall 24 of another axial bore 25 and a hollow inner conductor 26.

The novel input coupling means 17, typically brass, comprises a T-shaped member having a base leg 27 for introducing R.F. energy to the means 17, a first arm 28 for conducting coolant to the input means and a second arm 29 where the RF. energy and coolant meet and are transferred to the input transmission line 18.

The leg 27 for introducing RF. energy includes an RF. input center conductor 30, typically brass, input coaxial outer conductor 31 formed by the inner bore of leg 27 and an linsulating input center conductor support 32. To the leg 27 is attached a suitable connector such as an R.F. coaxial connector 34 including an inner conductive rod 35 and tubular insulating member 36, as of Teon tetrauoroethylene The first arm 28 for conducting coolant to the input coupling means 17 includes a modified flair union 37, a cooling fitting 38, a coaxial adapter end cap 39, typically brass, integral therewith and a dielectric pipe such as high alumina ceramic. A liquid tight seal is formed about a Kovar, for example, pipe seat 41, brazed to pipe 40, by means of an O-ring seal 42 to assure that the coolant will flow through the pipe 40.

The second arm 29 might be thought of as being divided into two abutting sections, a transformer section 43 where the RF. and coolant meet and a transmission section 44 where both flow together toward the transmission line 18. The transformer section 43 includes the end of pipe 40 and the vertical portion of a conductive elbow member 45, typically brass, and an outer conductor. The pipe 40 is disposed axially of the transmission line 18 and is adapted to receive the hollow inner conductor 21. The vertical portion of elbow member 45 is at right angles with respect to pipe 40 while the outer conductor is formed by adjacent portions of a coaxial adaptor 46, typically brass, soldered to end cap 39.

The transmission section 44 is adapted to transmit in fluid tight, and vacuum tight and electrically continuous fashion the coolant and RF. energy, respectively to the tube 11. It includes the horizontal portion of elbowed conductive member 45, sleeve member 47, as of Kovar, insulating spacer 48, RF. window 49, frame and washer 51 all axially bored so as to receive an external end portion of the inner conductor 21.

The end of the vertical portion of elbow member 45 is soldered to the input center conductor 30 while the horizontal portion serves as a conductor jacket for conductor 21 and sleeve member 47. Insulating spacer 48 is positioned within an opening in adaptor 46 and sandwiched between the elbow member 45 and RF. window 49. Window 49 is brazed to frame 50 which frame is brazed to annular projection 52 of a seat 53. Washer 51 is joined to window 49. The sleeve member 47 is sealed about the conductor 21 and at one end to washer 51.

For purposes of rigidity and alignment, the slanted midportion 54 of elbow member 45 receives a Kovar, for example, seat 55 for the pipe 40, which seat is brazed at one end about its inner periphery to a reduced end of pipe 40 and at the other end about its inner periphery to the youter periphery of conductor 21.

The means 17 is joined to the tube 11 in vacuum tight manner by soldering seat 53 to tube 11.

The output coupling means 23, wherein like numerals refer to like parts of the input coupling means 17, may be constructed similarly to input coupling means 17. It

is illustrated however, as having a vacuum flange member 56 sealed to the inner bore of leg 27 and a hollow inner conductor 30', so as to accommodate a different type RF. connector (not shown).

The coupling means were designed so as to maintain 50 ohm geometry throughout whereby losses due to irnpedance mismatch with external circuits are minimized. The leg may be at an arbitrary angle to the arms which may be at an arbitrary angle to each other. However, with the arms axially aligned and the leg at right angles thereto, mechanical considerations are simplified.

Referring to FIG. 3, wherein a typical frequency vs. VSWR plot for input and output coupling means of the type shown in FIG. l is illustrated, it may be observed that these coupling means are capable of rendering a consistent VSWR of less than 1.1 at frequencies from 0.5 to 1.() kmc.

Referring to FIG. 2, there is shown an alternate and preferred embodiment of the present invention. It includes a hollow T-shaped member 57 forming the coaxial adaptor. Leg 58 is threadedly secured or soldered at right angles to axially aligned arms 59, 60.

Disposed axially of the arms 59, 60 is an inner conductor 61 which has an axial bore within that portion of its length in arm 59. It serves as a conductor jacket for a sleeve member 62 disposed coaxially therein. Sleeve member 62 is in turn secured to an inner conductor 63. Inner conductor 63 comes from a tube (not shown), for example.

An insulating spacer 64 is positioned within an opening in the member 57 and sandwiched between conductor 61 and an R.F. window 65. The window 65 is held by a frame 66 brazed to the window 65, which frame is in turn brazed to `a seat 67. Washer 68 is joined to the window 65 and sleeve member 62.

Inner conductor 61 is secured by soldering to sleeve member 62 and has an elbow passage 68. Conductor 61 is centered within member 57 and adaptor flange 69 by means of insulating center conductor support 70.

Disposed axially within leg 58 is a dielectric pipe 71 having a `reduced end soldered to seat 72, as of Kovar, secured about the vertical opening elbow passage 68.

The pipe 71 has a hollow interior in communication with the inner conductor 63 whereby fiuid coolant may be transferred between an external coolant source (not shown) and the inner conductor 63.

The embodiment of FIG. 2 is similar to the embodiment of FIG. 1 except that the pipe 71 is disposed Within leg 58 approximately at right angles with respect to inner conductor 61. Improved results have been lnoted with the embodiment of FIG. 2 over those of FIG. 1.

While the coupling means of this invention has been described with reference to an electron discharge device of the slow-wave type employing fluid cooling internal to the slow-wave structure, it is readily apparent that the invention would have application wherever it is necessary to separate a fluid coolant in a conductor from R.F. energy being propagated thereon.

Since many changes can be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A coupling means comprising: a hollow T-shaped member forming an outer conductor; said T-shaped member having a pair of arms and a leg; a hollow inner conductor along which radio frequency energy may travel and through which a fiuid coolant may fiow disposed within one of said arms; a dielectric pipe through which a fluid coolant may flow disposed within the other of said arms and being in fluid communication with said hollow inner conductor; and, a second inner conductor along which radio frequency energy may travel disposed within said leg and being in radio frequency coupling relation to said hollow inner conductor, whereby radio frequency energy and fluid coolant may be separated within said coupling means with minimum perturbation.

2. The coupling means of claim 1 wherein said arms are axially aligned and said leg is approximately at right angles with respect thereto.

3. A coupling means comprising: a hollow T-shaped member forming an outer conductor; said T-shaped member having a pair of arms and a leg; a hollow inner conductor along which radio frequency energy may travel and through which a fluid coolant may flow disposed within one of said arms; a second inner conductor along which Iradio frequency energy may travel disposed within the other of said arms and being in radio frequency coupling relation to said hollow inner conductor; and, a dielectric pipe through which a fluid coolant may flow disposed within said leg and being in fluid communication with said hollow inner conductor whereby radio frequency and fluid coolant may be separated within said coupling means with minimum perturbation.

4. The coupling means of claim 3 wherein said arms are axially aligned and said leg is approximately at right angles with respect thereto.

5. A radio frequency means for coupling energy between a first transmission line and a second transmission line, said first transmission line adapted to be evacuated and having an inner and an outer conductor along which radio frequency energy may travel, said inner conductor having a hollow interior so as to provide therein passage for a fluid coolant comprising: a hollow T-shaped member forming an outer conductor and having a first and second arm and a leg; said first arm being coupled to and having an end sealed axially with respect to said first transmission line outer conductor; a hollow inner conductor along which radio frequency energy may travel disposed within said first arm; said first arm hollow inner conductor being radio frequency coupled and in fluid communication with said first transmission line inner conductor; a dielectric pipe through which a fluid coolant may flow disposed within said second arm and being in fluid communication with said first arm hollow inner conductor; a second inner conductor along which radio frequency energy may travel disposed within said leg and being in -radio frequency coupling relation to said first arm hollow inner conductor whereby radio frequency energy and fluid coolant may be separated within said coupling means with minimum perturbation; a radio frequency window sealed between said T-shaped member and said first arm hollow inner conductor; and, said window having an axial opening therein through which said first transmission line inner conductor may extend whereby a radio frequency permeable, vacuum-tight seal is formed for said first transmission line.

6. The means according to claim 5 wherein said arms are axially aligned and said leg is approximately at right angles with respect thereto.

7. A radio frequency coupling means for coupling energy between a first transmission line and a second transmission line, said first transmission line adapted to be evacuated and having an outer conductor and an inner conductor along which radio frequency energy may travel, said inner conductor having a hollow interior so as to provide therein passage for a fluid coolant comprising: a hollow T-shaped member forming an outer conductor and having a first and a second arm and a leg; said first arm being coupled to and having an end sealed axially with respect to said first transmission line outer conductor; a hollow inner conductor along which radio frequency energy may travel and through which a fluid coolant may flow disposed within said first arm; said first arm hollow inner conductor being radio frequency coupled to and in fluid communication with said first transmission line inner conductor; a second inner conductor along which radio frequency energy may travel disposed within said second arm being in radio frequency coupling relation to said first arm hollow inner conductor; a dielectric pipe through which a fluid coolant may flow disposed within said leg being in fluid communication with said first arm hollow inner conductor whereby radio frequency energy and coolant fluid may be separated within said coupling means with minimum perturbation; a radio frequency window sealed between said T-shaped member and said first hollow inner conductor; and, said window having an axial opening therein through which said first transmission line inner conductor may extend whereby a radio frequency permeable, vacuum-tight seal is formed for said first transmission line.

8. The coupling means according to claim 7 wherein said arms are axially aligned and said leg is at approximately right angles with respect thereto.

References Cited by the Examiner FOREIGN PATENTS 1,115,097 12/1955 France.

ELI LIEBERMAN, Acting Primary Examiner.

Z. ALLAHUT, Assistant Examiner. 

1. A COUPLING MEANS COMPRISING: A HOLLOW T-SHAPED MEMBER FORMING AN OUTER CONDUCTOR; SAID T-SHAPED MEMBER HAVING A PAIR OF ARMS AND LEG; A HOLLOW INNER CONDUCTOR ALONG WHICH RADIO FREQUENCY ENERGY MAY TRAVEL AND THROUGH WHICH A FLUID COOLANT MAY FLOW DISPOSED WITHIN ONE OF SAID ARMS; A DIELECTRIC PIPE THROUGH WHICH A FLUID COOLANT MAY FLOW DISPOSED WITHIN THE OTHER OF SAID ARMS AND BEING IN FLUID COMMUNICATION WITH SAID HOLLOW 